Method of consolidating metallic bodies

ABSTRACT

IN ACCORDANCE WITH THE INVENTION A METALLIC BODY IN PRE-PRESSED LOWER DENSITY FORM IS HEATED TO A TEMPERATURE SUFFICIENTLY HIGH FOR SUBSEQUENT CONSOLIDATION BY COMPACTION UNDER HIGH PRESSURE, THE HEATED BODY IS TRANSFERRED INTO A HEATED CONTAINER AT A LOADING STATION WHERE THE CONTAINED BODY IS EMBEDDED IN GRANULAR REFRACTORY MATERIAL, FOLLOWING WHICH THE HEATED CONTAINER AND ITS CONTENTS ARE MOVED TO A COMPACTION STATION AT WHICH THE BODY AND REFRACTORY MATERIAL ARE DISPLACED OUT OF THE CONTAINER INTO A DIE CAVITY AND THEREIN SUBJECTED TO COMPACTION UNDER PRESSURE SUFFICIENTLY HIGH TO CONSOLIDATE THE BODY TO IN EXCESS OF 95 PERCENT OF ITS THEORETICAL MAXIUM DENSITY.

Sept. 5, 1972 R. w. HAlLEY METHOD 0F CONSOLIDATING METALLIC BODIES Filed June 2, 1969 l lll MUDQOJUZU Z'NvE/v'roe. 05527' W HQ/Lss/ United States Patent Oce 3,689,259 METHOD OF CONSOLIDATING METALLIC BODIES Robert W. Hailey, Long Beach, Calif., assigner to Wheeling-Pittsburgh Steel Corporation, Pittsburgh, Pa. Filed June 2, 1969, Ser. No. 829,685 Int. Cl. B22f 3/14 U.S. Cl. 175-226 7 Claims ABSTRACT F THE DISCLOSURE lIn accordance lwith the invention a metallic body in pre-pressed lower density form is heated to a temperature suiiiciently high for subsequent consolidation by compaction under high pressure, the heated body is transferred into a heated container at a loading station where the contained body is embedded in granular refractory material, following which the heated container and its contents are moved to a compaction station at which the body and refractory material are displaced out of the container into a die cavity and therein subjected to compaction under pressure suiiiciently high to consolidate the body to' in excess of 95 percent of its theoretical maximum density.

BACKGROUND OF THE INVENTION In certain of its aspects the invention is directed to improvements over the process disclosed in Pat. No. 3,356,- 496, issued Dec. 5, 1967, to me on Method of Producing High Density Metallic Products. According to a specific contemplation of the patented process a metallic part to be consolidated is placed in a particulate or coherent heated refractory, e.g. ceramic, container and the container and body are introduced to a die cavity wherein both the body and container are subjected to compaction at high pressure required for consolidation of the metallic body.

SUMMARY OF THE INVENTION The present invention has in common with the patented process the treatment of a prepared body or prepress in the final consolidation stage under similar pressure, temperature and heat transference conditions, but improves upon the predecessor process with respect to preil'inal consolidation handlings and treatments given the prepress and granular material that ultimately becomes the refractory container during final consolidation.

As will later develop, although the patented process may include use of granular refractory material, the general procedure differs from the process herein contemplated as for example with respect to details of heating the prepress or body to be consolidated within a container followed by transference from the container of its contents into the compaction die cavity.

Among the benefits of the presently contemplated procedures are faster heating of charges, minimized refractory or ceramic contamination, and ceramic reclaimability by simple low cost operations. The invention achieves optimum control of consolidation temperatures, minimized start-up and down times, together with the employment of a heating and transfer system accessible at all times for maintenance and adjustment without causing serious down-time problems.

Objectively contemplated by the invention is the employment of flowable refractory grain as a medium for consolidation pressure transfer toL the work body. Frequently by adsorption, e.g. as in the case of alumina, the refractory grain becomes contaminated by moisture or other substances that can be volatilized from the grain.

Patented Sept. 5, 1972 According to the invention the grain is preheated at least to a temperature sufficiently high to drive olf volatile contaminants including adsorbed moisture. In order to reduce or minimize heat losses from the preheated work body to the embedding grain, preheating of the latter desirably is carried to higher temperature levels which may approximate the preheat temperature of the heated pre-pressed body. Thus the refractory grain may serve the dual functions of a compactible pressure transfer medium and also as a medium for preservation of preheat in the work body, thus to assure maintenance of necessary temperature levels for consolidation of the prepress.

Contemplated also is the employment of a technique involving use of a heated temporary container for initial reception of the preheated work body and embedding refractory grain, and transference of the container from what may be termed a loading station to a discharge or compaction station at which the contents of the container are displaced into the cavity of a high pressure resist-ant die for final consolidation of the workpiece. 'Ihus the container serves primarily as a material transfer means and itself need not be designed for high pressure resistance since application of the high consolidation pressure is confined to the die.

The materials and physical steps employed adapt to an operating sequence according to which the preheated work body which has been pre-formed to a unitized state at relatively lower density, is introduced to the heated container at a loading station followed by introduction to the container of a measured quantity of the refractory grain. This procedure may involve also the removal and return of a heated container closure, all in timed relation with the container loading, transference of the container to the die location, and finally displacement of the container contents into die cavity, all as will later appear. Pre-packing of the refractory grain may occur at the loading station and be accomplished by a plunger sized to enter the container with its cover removed.

After shifting of the container into overlying alignment with the die cavity, a vertically reciprocating punch displaces both the grain and work body including the bottom layer of grain, down into the die cavity wherein continued travel of the punch subjects the body to high pressure compaction by pressure transfer through or within the grain, the temperatures and pressures employed being, as previously indicated, suflicient to consolidate the body to a density increase in excess of percent, and most usually closely approaching percent, of the theoretical maximum density.

Thus because of the physical state of the facilities employed, including notably the use of freely owable refractory grain and quick shiftability of the heated container, it is possible to achieve high production rates of a wide variety of consolidated metallic products in equally varied sizes, shapes and particular compositions.

The invention will be further understood from the following detailed description of the accompanying drawing which is illustrative diagrammatically of typical operating sequences in keeping with the invention:

DESCRIPTION OF THE PREFERRED EMBODIMENT The process may be regarded generally as comprising means indicated at 10 for feeding refractory grain from a supply source 10 into a container 11 at the designated loading station at which the container also receives the heated prepress 12, following which the loaded container is transferred to the designated consolidation station beneath punch 13 and in alignment with a die cavity 14 which receives the packed embedding grain and the preformed body itself as a result of displacement out of the container 11 by the down traveling punch 13.

It is to be understood that the supply source as indicated at is to be regarded merely as illustrative of any suitable means for controllably delivering the grain to the system, either in heated or unheated condition. Where, as most usually, the grain will be given some degree of preheating, the heat may be supplied by elements 24 embedded in the grain at spacing sufficiently close to assure efficient and uniform heating of the grain.

Useable refractory grain materials may be characterized as comprising any of or mixtures of the ceramics, refactory compounds, carbon, and graphite. The term ceramics is intended to include those chemically combined metal compounds and compositions which have come to be characterized as ceramics. The latter include such metallic oxides as oxides of any of silicon, aluminum, barium, calcium, magnesium, thorium, and zirconium, as well as such oxide complexes, as of combinations of any of silicon, calcium, or magnesium oxides that exist in earths and clays; also metallic sulfates, e.g. sulfates or barium or calcium; aluminates, e.g. aluminates of calcium or magnesium; silicates, e.g. silicates of aluminum,

' calcium or zirconium; and such fiuorides as calcium uoride. The term refractory compounds is intended to include those high melting point inorganic compounds not always characterized as ceramics, including the nitrides, borides, carbides, silicides, and suldes of both metals and nonmetals, in the form of simple or complex compounds. Binders need not be added to the refractory grain. However, binders may be added if they do not interfere with the flow and packing of the grain, are not contaminative to the consolidated product, and provide positive advantages such as minimizing the loss of refractory grain in the transfer operations.

A practical size of refractory grain for this process is in the range of 325 mesh to 100 mesh grain, although coarser and liner grain and mixtures may be used for special purposes. Finer grain tends to dust and may not pack to as high a density as coarser grain. Coarser grain usually penetrates more deeply into the surface of a part being consolidated than does a iiner grain, making surface clean-up more diicult. It may be desirable in some cases to use controlled mixtures of particle sizes in Order to obtain the best total grain characteristics.

The grain may be preheated or not, depending mainly on: the size and configuration of the part to be consolidated; desire to limit the cost and complexity of grain ltransfer mechanisms; the rate at which parts are to be consolidated; and chemical purity considerations, as described in more detail below. If the grain contains volatiles that may be damaging to the part being consolidated (such as water vapor), it can be preheated in a separate operation to remove the volatiles, and stored under clean, dry conditions until used, or the grain may be preheated directly prior to loading into the hot transfer container.

For larger billets and solid parts, where grain volume is small relative to part volume, it may be most practical and economical not to preheat the grain to a high temperature before loading the grain into the hot transfer container and around the part. Under these circumstances, the later described hot transfer container and/ or the hot part will provide the heat capacity for bringing the grain to a satisfactory temperature prior to or during consolidation. The major factors influencing heating procedures here would be: the grain volume relative to part volume, the thermal conductivity of the part to assure that heat lost from the part surface to the surrounding grain will be replaced rapidly by heat ilow from the internal mass of the part without creating undesirable temperature gradients in the part; the ability of the part to be brought to a higher temperature than needed for consoli dation to provide the extra heat capacity for heating the grain; and the ability of the grain to ow and deform properly to distribute consolidation pressures under less than fully hot conditions.

For smaller shaped parts, hollow parts, and parts which are to be consolidated at a maximum rate with assured temperature control, major advantages are gained by preheating the grain to a high temperature corresponding to the part consolidation temperature or above, before loading the grain into the transfer container. This procedure can eliminate volatiles, prevent loss of heat from the part prior to consolidation, and provide for a faster ow of parts through the process with a Smaller parts handling system. It also minimizes contact time between the grain and the -part to be consolidated, at the high temperatures where surface reactions can occur.

Normally, for consolidation of iron and other similar melting point alloys, a fused aluminum oxide grain of minus 100 mesh grain size provides satisfactory characteristics for this process. It is resistant to self bonding and sintering when owed over a hot hearth for the purpose of preheating. It packs well by vibration or tamping around a part to be consolidated (usually to a density about 50% of theoretical) to provide a firm external and internal support for the part during transfer operations. During consolidation at temperatures in the order of 1900 to 2300 F., it ows by crushing and deforming to a density of about of theoretical, the final density being primarily dependent on the particular grain material used, its particle size and distribution, and the ternperature and pressure of consolidation. As both the part and the grain are compressed longitudinally in consolidation, the grain ows to distribute pressures uniformly enough so that the part is consolidated to a density at or near theoretical density.

In consolidation, the cross-sectional conguration of the part is essentially maintained while the length of the part is reduced in proporation to the change in density. Enough open continuous porosity normally is maintained in the grain to permit the escape of gases from the part being consolidated. The fused alumina grain is relatively inert chemically to most metals at temperatures up to about 2200" F., and after consolidation and ejection from the die, the grain breaks and sandblasts away readily from part surfaces. During consolidation, the grain acts as a satisfactory thermal barrier to prevent heat ow from the part to the die, so that the part develops uniform consolidated properties throughout its mass.

With many products, the lower hardness and greater deformability of silica (SiOz) at elevated temperatures can make it advantageous to use silica or a similar material as a refractory grain. For very high temperature consolidations (such as the refractory metals and refractory compounds), it can be advantageous to use materials such as thorium oxide, zirconium oxide, boron nitride, carbon, etc., as simple compounds or in combination with other refractory materials, to provide better properties in consolidation than to lower melting point refractory grains. Where it may be necessary or desirable to remove refractory grain material from a consolidated part by chemical means, or to provide other particular properties, acid soluble refractory grain such as magnesium oxide or calcium oxide may be used.

:In reference now to the prepress y12 whose composition determines that of the nal consolidated product, the general powder compositions which can be consolidated into products using the loose grain method include the following: pure or blended elemental powders, e.g. Mo, Fe, W, Ni, Cr, Co, etc.; prealloyed powders, e.g. stainless steel; ceramic and refractory compounds such as metal oxides, carbides, borides, nitrides, etc.; metal-ceramic, metal-carbide, etc. mixtures, e.g. Fe alloy plus aluminium oxide addition; and combinations of materials as cores and claddings, fibers and powders. Binders may be used if compatible with heating techniques and the iinal required properties of the product.

The particle size of the powdered material may be that employed in conventional powder metallurgy, and may vary from less than 1 micron average diameter up to about 30 mesh or larger.

fProducts which are to be consolidated by the loose grain process must have a preliminary product form which will retain its shape and integrity during heating and handling, prior to enclosure in the refractory grain. Typical methods used to provide preformed products include: IPowder is packed in a container (such as atomized superalloy powder of high hardness packed in a formed metal container or in a sprayed or cast metal or ceramic container); powder is packed in a container or mold and presintered to provide preliminary properties or initial diffusion before consolidation (such as electrolytic tungsten powder packed and presintered in a split ceramic mold); powder is pressed to a preliminary product form with or without a container (such as iron alloy powder isostatically pressed in an elastomer mold to a gear or other form, or tool steel powder pressed inside a tubular container in a steel die); powder is pressed to a preliminary product form with or without a container and presintered prior to consolidation (such as a stainless steel composition blend of elemental powders which will benefit from a diffusion heat treatment before consolidation).

The temperature to which the material to be consolidated is heated depends on: the composition and form of the product; the consolidated properties desired (such as metallurgical structure, strength, density, etc.), the unit pressures available in consolidation; potential reactions with the refractory grain; and the rate of product flow desired through the process. In general, it is desirable to consolidate at the highest safe temperature that is compatible with obtaining the density, properties, and quality required in the final product. A refractory grain normally can be selected which allows satisfactory consolidation in line with these considerations. The examples below illustrate how specific consolidation temperatures may be chosen:

(a) For some alloys such as Ti-Al-V alloys, it can be desirable to consolidate at a temperature below about 1825 (roughly 62% of the temperature at which the alloy begins to melt) in order to maintain an alpha structure. Unit pressures in the order of 35 t.s.i. (tons per square inch) should be available if consolidation to full density is to be accomplished at 1-825. A following heat treatment may be necessary to develop the full properties of the alloy.

`(b) Some of the superalloys (such as the nickel and cobalt base alloys) have high strength and resistance to deformation at temperatures close to their melting points. With these alloys, full densities and good properties can 'be obtained by consolidation in the range of 2lO0-2300 1F. (roughly 90-98% of the temperature at which melting begins), using pressures of about 35 t.s.i.

(c) With prealloyed stainless steel powders, full densities and good properties are obtained by consolidation at 200G-22.00 F. (roughly 75-85% of the temperature at which melting begins), using pressures of about 30 t.s.i.

(d) With stainless steels made from blended elemental powders such as iron, nickel, chromium, and molybdenum, preheat temperatures of '2300-2400" F. (roughly 85-95% of the temperature at which melting begins) will speed diffusion of the alloying elements and allow a `faster flow of product through the process. Consolidation still may be carried out at a low temperature in the order of 2000-2200 F., for handling or other reasons.

(e) With tool steels and alloy steels made from blended elemental powders, the major factors determining preheat and consolidation temperatures include: the particle sizes of powders used; the properties desired in the product; the rate of product -ow desired; and the best conditions for reduction of oxygen in the powders by excess carbon in the blended mixtures. Normally, these alloys will be preheated to 2200-2400 F. before consolidation (roughly 75-95% of the temperature at which melting begins), with consolidation at about 2200 F., using pressures around 30 t.s.i. or higher.

(f) With a refractory metal such as molybdenum, consolidation to over 99% of theoretical density has been accomplished at a temperature of about 3000 F. (63% of melting point), using pressures around 35 t.s.i. held Ifor only a fraction of a second. Other tests indicate that to consolidate tungsten in a matter of seconds to a density near theoretical will require consolidation temperatures in the order of 3300 F. (54% of melting point) and pressures around 35 t.s.i.

Some or all stages of the process may operate in a controlled atmosphere, the composition of which is predetermined in accordance with such factors as materials employed and their behavior at temperatures to which they arc exposed. Accordingly, in the drawing I have indicated at 15 the general outline of an enclosure within which may be accommodated the various stages of the process.

A number of gases may be used for atmospheres in the process, including inert, reducing, oxidizing, carburizing, nitriding, and neutral gases. They may be used separately or as mixtures. Their normal purpose is to protect the heating equipment, the refractory grain, and/ or the product being consolidated. The choice of a specific atmosphere for heating and consolidating a specific product will depend primarily on certain gas properties such as: chemical reactivity or inertness in relation to the product and/ or the refractory grain; solubility in the product; thermal conductivity; density; ability to be purified; convenience :relative to use and preventing contamination; and cost.

Argon is an example of an inert gas available in quantity in a high purity form at an acceptable cost. Argons high density and atomic weight, and its large atom size are favorable properties for the design of heating and transfer equipment to avoid leakage and contamination by other gases. Argons low thermal conductivity can decrease heat loss from the product after it has been brought to temperature and during transfer operations. It is a true inert gas, is non-explosive and can be purified satisfactorily for recirculation.

Hydrogen is an example of a reducing gas available in pure form in quantity at an acceptable cost. Hydrogen will dissolve in and/or react with many materials (e.g., titanium, zirconium, carbon, boron), and its use with such materials may require special techniques or protective measures. Its low density and atomic weight provide problems in preventing back diffusion of air into hydrogenfilled enclosures or equipment. Its high thermal conductivity can greatly increase insulation requirements for heating equipment, and cause rapid heat loss from the surface of a hot part as it is transferred from a heating station. Hydrogen is explosive when mixed with relatively small quantities of oxygen. lIt can be purified readily, and is considerably lower in cost than argon.

Other gases that may be used in the process are gases such as helium, nitrogen, dissociated ammonia, carbon monoxide, the endothermic and exothermic gases, hydrocarbons, etc., used separately or mixed to provide specific properties.

For some applications, it could be desirable to preheat the product prior to consolidation in a partial or full vacuum to help remove gaseous reaction products (e.g., carbon monoxide and carbon dioxide from the reduction by carbon of oxides in a powder mixture), or to help remove volatile products such as sulfur. For most products, it appears most practical to carry out the final transfer and consolidation steps in a gas atmosphere rather than in avacuurn.

Again in reference to the drawing the refractory grain is shown to be fed under control as by release gate 16 into the transfer container 11 to a depth suiiicient to fully embed the preheat 12. Initially a quantity of the grain may be introduced to the container to a depth suiicient to form a bottom layer L which subsequently is displaced out of the container together with the grain and prepress charge at the consolidation station. Plunger 17, which may or may not be heated, operates to compact the layer L by descent into the open top container, and also to pack 7 the grain over the prepress 12. Upon completion of the container loading, its cover 18 is shifted to close the container and its contents. If desired, provision may be made as indicated by heating units 19 and 20 for heating the container with or without continuance of the heating to its arrival at the consolidation station. For transference of the heated prepress suitable means such as tongs 21 may be used and Where conservation of the prepress heat may be important, a surrounding heating means 22 may be provided. Thus at the completion of loading, the closed container 11 is shifted to the consolidation station in vertical alignment Iwith the punch 13 and die cavity 14.

The transfer container can potentially be loaded for transfer operations at temperatures ranging from room temperature to roughly the temperature of the prepress. In choosing a material for the transfer container, factors to be considered are: heat capacity; thermal conductivity; strength and stability at the maximum temperature of use; hardness and erosion resistance; physical and thermal shock resistance.

For large parts and billets, the transfer container may either be unheated or heated to an elevated temperature up to about the temperature of the part. Lower transfer container temperatures can improve handling convenience, allow a wider `range of container material choices, and provide better container life. However, with an unheated or low temperature transfer container, the refractory grain and/or the hot part must have enough heat capacity to provide satisfactory grain and product temperatures for consolidation, and it becomes more desirable to use fast transfer speeds. Stainless steels may be suitable for use up to about 1000 Inconels and similar oxidation resistant alloys can be suitable up to temperatures of about 2200 F. Higher melting point materials such as molybdenum and pyrolitic graphite can be used for higher container temperatures.

For smaller parts and the most eicient process flow, it normally will be desirable to maintain the transfer container at an elevated temperature to minimize heat loss from the part. The smaller size of the container in these circumstances makes possible the use of materials not always available in large forms, including tungsten, va-rious ceramics, and the refractory compounds.

In the consolidation stage, after the container 11 is moved over the die cavity 14, descent of the punch 13 displaces the grain pack G and part 12 down out of the container into cavity 14, during which displacement the die plunger 23 also is displaced down against the nominal back pressure employed to bring the plunger to its illustrated position and support the weight of the charge to be consolidated. While not shown, any of various forms and compositions of die cavity liners may be used as shown for example in my Pat. No. 3,356,496. Upon completion of the part consolidation, elevation of the plunger displaces the grain charge and part 12 up out of the die cavity.

The general range of pressure application rate by punch 13 to the embedded body 12 after displacement into the die cavity 14 may be from l1/240l per second. For large volume product possibilities such as the iron, nickel, and cobalt base alloys, successful consolidations have |been carried out with pressure application (ie. punch travel) rates in the order of 2-6 inches per second.

The primary purpose of a fast rate of pressure application is to reach full consolidation pressure and full compaction of the product while the refractory grain and product are at a desired high temperature. However, the rate of pressure application also should be slow enough so that gases existing in a free state in the product and refractory grain are satisfactorily expelled as the product and grain are compacted.

Stainless steel alloys have been consolidated to full density in alumina grain at pressures ranging from 25-35 t.s.i. Other hard alloys such as the stellites, superalloys and hastelloys also have been consolidated to full density at 35 t.s.i. With lower melting point, lower strength alloys of metals such as aluminum and copper, and with lower melting point refractory grain, it is believed that satisfactory consolidation can be accomplished at pressures as low as 10 t.s.i.

The following are illustrative procedures and materials employed in accordance with the invention:

In keeping with the drawing description as being diagrammatic, reference numerals are omitted in the examples as to various steps and operations which are known in the art, for example preparation and preliminary compacting of the body to be consolidated, particularization of the shape of the prepress and its accommodation within a precompa'ction die or can, and the use of a protective liner within the die cavity 14. It will be understood that the die cavity expression used in the claims is intended to be inclusive of a lined or unlined cavity.

EXAMPLE 1 A 40 pound M-2 tool steel billet can be prepared by the loose grain consolidation method using a 700 ton press and a powder mixture containing:

Iron, 79.0%, as 20 micron powder Chromium, 4.0%, as l0 micron powder Vanadium, 2.0%, as 10 micron powder Tungsten, 6.5%, as 3 micron powder Molybdenum, 5.0%, as 3 micron powder Carbon, 1.5%, as minus 325 mesh lampblack Carbon is added in this alloy in excess of the normal amount in order to help reduce oxides in the powders, and to increase the hardenability of the final alloy.

The above powders are blended and milled together in an argon atmosphere to obtain a uniform, intimate mixture free from external contamination. After milling, the powder mixture is pressed at room temperature into a 4% diameter by 14 long cylindrical shape in a die, using a pressure of 20 tons per square inch. A steel tube with a 0.060 wall thickness is used in this case inside the die to hold the powder in an integral form after pressing. At 20 tons per square inch, the powder presses to a density of 75% of theoretical.

Induction heating in an argon gas atmosphere is used to bring the pressed billet form in its steel can to a ternperature of 2300 F. The billet, supported on a 11/2 thick by 5 diameter cast alumina base, is held at 2300 F. for one hour to obtain a desired level of solid solution between the alloying elements prior to consolidation, and to permit reduction of residual oxides by the carbon. When the preheat cycle is complete, the billet typified by the shape 12, although not tubular is immediately raised out of the can and transferred into a 5" I.D. cylindrical transfer container 11 of Inconel maintained at about 2000 F. Preheated 100 mesh alumina grain from the container or heating zone at a temperature of about 2000 F. is poured rapidly into the annulus between the container and the billet. In less than 10 seconds, the hot alumina is packed to a total height of approximately 17" in the container, with a packed density about 50% of theoretical.

At this point, the consolidation die 14, containing an expendabble 0.040 thick split steel liner backed up by a graphite-greased paper liner, is positioned outside the press to receive the hot charge. The transfer container is moved over the consolidation die, and the billet 12 and alumina grain G are lowered rapidly into the lined die. The die then is moved directly into the press under the punch 13, where a pressure of 700 tons consolidates the -billet to a 4% diameter by lOl/2" long cylinder and to full density, and the alumina grain to -90% of theoretical density. Pressure is held for a period of 15 seconds to obtain maximum compaction and high diffusion bond strength.

The pressure then is released, the die moved out of the press, and the compacted billet and ceramic ejected with the die liner. Impacting the liner breaks up the alumina and frees the billet from the liner so that it can be processed through heat treatment and following Working steps to final product form and desired properties.

EXAMPLE 2 A 2'1/2" pipe cap (or other similar pipe fitting) of titanium alloy can be made by the loose lgrain consolidation method, using a 700 ton press and a prealloyed powder. A typical alloy is Ti-6Al-4V, which provides high strength, high corrosion resistance, and low weight for aircraft applications.

The above alloy is obtained as a high purity powder in a minus 100 mesh particle size, and is pressed directly at 20 tons per square inch to a preliminary pipe cap form and a density of about 65% of theoretical. To obtain a controlled repetitive pressing of the pipe caps I.D. and O.D. configuration, the powder is packed to a standard density of about 45% of theoretical in a urethane mold, which then is sealed and isostatically pressed. For maximum protection against oxidation, the powder may be loaded and packed in the mold under an argon or nitrogen atmosphere. As pressed, the cap cross-section is approximately that of the nished part, but the length is about 1% times the desired lfinal length.

The pressed part is heated by induction in a pure argon atmosphere to a temperature of 1800 F. (below the alpha transformation temperature). When it has reached a uniform temperature, it is transferred rapidly with 1800 F. tongs 21 to a 5" I.D. cylindrical transfer container 11 of Inconel maintained at 1800 F. Immediately prior to this move, the bottom of the transfer container is loaded with a 1" layer L of 1800 F. preheated 325 mesh alumina grain packed to a firm density of about 50% of theoretical. The pressed part is laid open end up on this alumina bed, and additional 1800 F. preheated alumina grain is poured rapidly ofver the part and packed firmly to a height l over the top of the part.

At this point, the consolidation die, containing an expendable 0.020" thick split steel liner backed up by a graphited paper liner, is positioned in the press to receive the hot charge. The transfer container 11 moves over the consolidation die, and the press punch 13 immediately moves down through the container to transfer the ceramic and contained part to the lined die cavity, and to apply a pressure of 700 tons in the die. At this pressure, the pipe cap consolidates to full density and nal form, and the alumina grain compacts to 75-85% of theoretical density. Pressure is held for a period of 15 seconds.

The pressure then is released, the die moved out of the press, and the compacted billet and ceramic ejected with the die liner. impacting the liner breaks up the alumina around the O.D. of the pipe cap and frees it from the expendable liner. Sandblasting removes the remaining alumina grain from the LD. and O.D. of the pipe cap,

and leaves it ready for following heat treatment, sizing, and final machining.

I claim:

1. The method of consolidating a metallic or ceramic body that includes:

(a) heating said body in lower density form to a temperature suciently high for consolidation in step (f) by compaction -under high pressure,

(b) transferring said heated body into a container,

(c) flilling granular refractory material into the container to contact and embed said heated body there- 1n,

(d) aligning the container with a die cavity,

(e) displacing the refractory material together with the heated and embedded body into said cavity in contact with its wall, and

(f) compacting said refractory material and the embedded body under high pressure and thereby consolidating the body to higher commercial product density.

2. The method of claim 1 in which said refractory material is passed through a heating zone wherein the material is preheated to a temperature sufficiently high to vaporize contaminating moisture.

3. The method of claim 2 in which said material is preheated to substantially the temperature at which said body is consolidated.

4. The method of claim 2 in which the container is preheated to elevated temperature.

5. The method of claim 1 in which the container is positioned at a loading station for reception of said body and granular material and is then shifted to its position of alinement with the die cavity.

6. The method of claim 5 in which a layer of said granular material is preliminarily introduced into the bottom of the container at the loading station.

7. The method of claim 5 in which said granular material is passed through a preheating zone before introduction to the container, the container also is preheated, and the container contents are displaced at the shifted position of the container by vertically reciprocating punch down into the die cavity underlying the container.

References Cited UNITED STATES PATENTS 3,344,209 9/ 1967 Hague et al. 715-226 3,356,495 12/ 1967 Zima et al 75-226 3,356,496 12/ 1967 Hailey 75-226 3,469,976 9/ 1969 Iler 75-226 REUBEN PSTEIN, Primary Examiner 

